Oxy-combustion is an energy conversion technique utilized in certain industries requiring high combustor firing temperatures, such as metal smelting, glass making and hazardous waste disposal.
In order to achieve higher combustor firing temperatures, the fuel is burned in a presence of an oxygen-rich stream rather than using conventional air, which is only about 21% oxygen by volume. The oxygen-rich stream fed into the combustor is produced by processing conventional air through an air separation unit, which removes the nitrogen from the air, which is about 78% of the volume.
Oxy-combustion yields flue gas which is predominately formed of carbon dioxide, as compared to conventional air-fired combustion wherein the flue gas is predominately formed of nitrogen. As a result of the reduction in nitrogen in the flue gas, the production of nitrogen oxides (NOX) as a result of the combustion process are greatly reduced. In addition, the carbon dioxide may be captured and sequestered.
Combustion of fuel in an environment with nearly pure oxygen also results in a substantial rise in the combustor firing temperature to about 3,500° C., often which cannot be sustained by the combustor which may be ordinarily designed to operate at about 2,000° C. As a result, recirculation of the flue gas in oxy-combustion may be used to reduce the combustor firing temperature to a lower level. Thus, as may be understood, the oxy-combustion process may enable adjustment of the combustor firing temperature by varying the carbon dioxide recycle rate to control the volume of diluent gas to achieve higher or lower temperatures.
As such, several key attributes of oxy-combustion, particularly the elimination of nitrous-oxides and high concentration of carbon dioxide in the flue gas, are prompting interest in oxy-combustion for power generation with integrated carbon capture. These characteristics are advantageous for meeting emissions requirements and potential greenhouse gas mandates by minimizing the economic impact of carbon capture. However, these advantages are currently balanced by the cost and auxiliary power requirements required to provide near pure oxygen to the combustor using current air separation techniques.
Unfortunately, before captured gaseous carbon dioxide can be sequestered, it must be compressed. In order to provide a more efficient system, the present disclosure makes use of supercritical carbon dioxide oxy-combustion. Furthermore, coupling supercritical oxy-combustion with a supercritical carbon dioxide power generation block as disclosed herein offers several technical advantages that could reduce the cost of electricity, such as compact equipment which could minimize capital costs and high thermal efficiencies which reduce fuel requirements and operating costs. Supercritical oxy-combustion enhances this by offering high combustion efficiencies, compact combustors, and a high quality flue gas at near pipeline pressures suitable for carbon sequestration, enhanced oil recovery, or as a source of carbon dioxide for commercial utilization.